The magnetron held by the University of Melbourne’s School of Physics stemmed from the development of radar. During the Second World War radar developments were made by the Division of Radio Physics located in Sydney [i]. With such a large coastline to protect, the Australia Government had allocated time and funds to researching methods of shore protection. Along with the guidance of British radar development, Australian scientists developed ways of detecting enemy vessels arriving via the ocean.
This particular magnetron was created in 1944 at the Council for Scientific and Industrial Research (CSIR) Valve Laboratory located within the University of Melbourne. The development of the instrument was overseen by Leslie Martin (1900 - 1983) and fellow physicist Eric Burhop (1911 - 1980). Martin was Officer in Charge of the Valve Laboratory in 1942, the first year the laboratory operated at the University of Melbourne. He took the position again in 1944 shortly before becoming Professor of Physics.
Through its construction this particular object represents the period in which it was made. Due to Australia’s involvement in the Second World War scientists often lacked the supplies that they needed. For this reason the magnetron incorporated an external copper cylinder for the body of the tube, a material not normally used for this purpose [ii]. After its development was complete samples of its technology were manufactured by three companies; The Wireless Valve Company, Metal Manufacturers and the laboratories of the Post Master General [iii].
The magnetron is a device which generates or amplifies high frequency electromagnetic waves. The geometry of the device together with the crossed electric and magnetic fields coerces electrons to bunch
together and follow cycloidal paths outside the magnetron cavities.
In the cylindrical magnetron a radial electric field is created by applying a voltage between the central cathode and the outer anode. Superimposed on this field is a radio frequency field and combined with the guiding perpendicular magnetic field the magnetron transfers energy from the D.C. battery to the radio frequency field.
The magnetron was essential to the development of radar during the second world war as it was the only reliable means of producing microwaves of the high power necessary for early radar devices.
Jacqueline Eager
Student Projects Placement, Cultural Collections 2005
i'Laby Era in 10 Minutes', Laby Files, Physics Museum's archive, University of Melbourne, p.2.
ii CSIR/Melbourne University Valve Laboratory, Physics Museum's archive, University of Melbourne, p.1.
iii 'Technology in Australia 1788-1988' http://www.austehc.unimelb.edu.au/tia/914.html, accessed on 26.09.2005.
Three Dimensional Object (requires Quicktime): 18-1.obj
3 cm dia oxidised copper cylinder held in construction jig (consisting of two flat square steel slabs clamped with bolts). Three copper through glass electrodes radiate out from the magnetron cylinder. Two of these tubes are small and adjacent to each other (filament leads).
Three Dimensional Object (requires Quicktime): 19-1.obj
Copper magnetron with disc-like body has three radiating electrodes each emerging through a copper to glass tube. Two of these are arranged on one side(= filament leads) and the other larger tube (collector/anode) is arranged diametrically opposite.
Three Dimensional Object (requires Quicktime): 20-1.obj
Part of magnetron case consisting of a hollow baseless copper cylinder (similar to Reg. No. 18). Copper vanes are arranged spoke-like inside body. Three glass tubes radiate out of the body (similar to Reg. no. 20).
Three Dimensional Object (requires Quicktime): 21-1.obj
An electrometer is a device for measuring quantity of electric charge. In the string electrometer an electrode, to which a lightweight mirror is attached, is suspended on a quartz fibre. The electrode forms one plate of a capacitor. Any charge deposited on the electrode tends to rotate the mirror. A light beam reflecting off this mirror is deflected and the deflection is proportional to the deposited charge.
The string electrometer was originally designed by Horace Darwin and Professor T.H. Laby in conjunction with Darwin’s Cambridge Instrument Company. This particular apparatus was constructed in April 1918 and is considered to be an improvement on its predecessors due to its rapid response time of less than one tenth of a second. Although some say it was also the string electrometers sensitivity that made it significant, Laby disputed this belief as he felt that it was possible to increase the sensitivity of existing instrumentsi .
Former Head of Physics, Ed Muirhead recorded a number of occasions where the string electrometer was featured. One of these was in 1909 at the Royal Society Soiree. At this event the string electrometer was used to ‘demonstrate the detection of single alpha particles from a radioactive source’ii . Laby appears to have been proud of this exhibition stating that he saw it as ‘the first occasion on which the counting of atoms electrically had been shown publicly’iii . Muirhead also recounts how the instrument was sent to Australia in 1914 for the British Association for the Advancement of Science meeting.
Jacqueline Eager
Student Projects Placement, Cultural Collections 2005
iLaby, T.H., A String Electrometer, Physics Museum Archive, University of Melbourne, p. 113.
iiMuirhead, E., A Man Ahead of his Times: T.H. Laby's Contribution to Australian Science, Science Spectrum Publications, Melbourne, 1996, p.4.
iiiString Electrometer, Physics Museum Archive, the University of Melbourne, p.1.
Three Dimensional Object (requires Quicktime): 78-1.obj
Declination instrument consisting of metal horizontal cylinder erected on brass three legged stand. A wooden rectangular box forms part of the instrument from which a horizontal telescope emerges (measurement of geographical meridian) and a vertical glass tube containing the suspension for the hollow magnet.
Three Dimensional Object (requires Quicktime): 80.obj
Dip circle consists of a brass cylinder with two glass flat end-windows, containing a centrally mounted magnetic needle free to rotate about its supporting axis in a vertical plane. The needle , when at rest is arrested by a trunnion from which the needle can be raised by means of external knob. Very close to the needle is mounted the vertical circular scale. Two magnifiers are mounted at the end of a brass “diameter’ which can be rotated so as to read off the angular positions of both ends of the needle after being set up. Graduated horizontal scale on the base. Spirit level mounted. Tribach base.
Three Dimensional Object (requires Quicktime): 81.obj
Dip circle has much the same elments as in the previous model ( cat. no.81), except the brass cylinder is replaced by a mahogany box with two end windows. Tribrach base is fixed into a wooden sheet ( maybe for ease of carrying in the field).
Three Dimensional Object (requires Quicktime): 82.obj
Brass quadrant electrometer consists of four quarter-cylindrical brass boxes (quadrants ) each mounted on a glass insulating pillar. The whole is housed within an electrostatic shield (Faraday cage) - a beehive shaped wire cage enclosure (aka a “bird cage”). The quadrants and cage stand on a round base platform on three legs with levelling screws (tribach base?). Arising from the platform is a separate vertical rod arises from the periphery and terminates over the axis of cylindrical symmetry and from which provision is made for a conducting suspension fibre which supports the horizontal “paddle” which is free to rotate within the cylindrical cavity of the four quadrants. The suspension and paddle are unfortunately missing.
Three Dimensional Object (requires Quicktime): 83.obj
Brass and glass case enclosing two sets of coils; surmounted by a vertical rod on which a compensating (?) magnet may be moved either vertically or rotated in a horizontal plane; 3 levelling screws and spirit level.
Three Dimensional Object (requires Quicktime): 84.obj
Last used in a Physics 2 experiment in the 1940-50s. Refer to the printed version Part 2 Laboratory Manual (ed. Natalie Allen) for further details. Likely acquisition in early 1900s by Lyle?? (Research on instrument makers catalogues has not been undefrtaken Photographed June 2003 (Nicola)
Three Dimensional Object (requires Quicktime): 279-1.obj
Wooden cube with 8 metal screws visible on the upper and lower faces, securing sides together. The upper face of the cube is plastic. Metal apparatus, possibly brass, fixed to the upper face, All of the faces of the wooden cube, apart from the upper plastic face, have been sanded smooth and on all faces but the lower face, a finish has been applied.
Wood cut and dove tailed, screwed and adhered; plastic moulded, screwed and adhered. Metals cast, forged, machine cut, screwed and adhered. Wood coated (painted varnish).
History of object: The “Part III” label indicates it was used in the third year undergraduate labs.
No. of pieces: one object recessed into wooden box with detachable parts. Handmade wooden box enclosing a machine molded solid metal object. Plastic machine molded attachment.
Gold electroplated metal, wax-matte hand polished wooden box, plastic has either been polished or had a varnish polish added to the surface.
Detachable brass elliptical stopper, two brass butterfly screws, two hook latches attached to outside of box to secure object for transport.
Polished wood surface, possibly wax coated. Brass metal coated with gold patina/electroplating. Plastic component either polished or coated with gloss varnish.
Body possibly cast with additional components welded.
Exterior surface of cylindrical body has been painted.
Surface finish: evenly applied black coating on exterior of cylindrical body.
